CVE-2020-16944 in SharePoint Server
Summary
by MITRE • 10/17/2020
<p>This vulnerability is caused when SharePoint Server does not properly sanitize a specially crafted request to an affected SharePoint server.</p> <p>An authenticated attacker could exploit this vulnerability by sending a specially crafted request to an affected SharePoint server. The attacker who successfully exploited this vulnerability could then perform cross-site scripting attacks on affected systems and run script in the security context of the current user. These attacks could allow the attacker to read content that the attacker is not authorized to read, use the victim's identity to take actions on the SharePoint site on behalf of the victim, such as change permissions, delete content, steal sensitive information (such as browser cookies) and inject malicious content in the browser of the victim.</p> <p>For this vulnerability to be exploited, a user must click a specially crafted URL that takes the user to a targeted SharePoint Web App site.</p> <p>In an email attack scenario, an attacker could exploit the vulnerability by sending an email message containing the specially crafted URL to the user of the targeted SharePoint Web App site and convincing the user to click the specially crafted URL.</p> <p>In a web-based attack scenario, an attacker would have to host a website that contains a specially crafted URL to the targeted SharePoint Web App site that is used to attempt to exploit these vulnerabilities. In addition, compromised websites and websites that accept or host user-provided content could contain specially crafted content that could exploit the vulnerability. An attacker would have no way to force users to visit a specially crafted website. Instead, an attacker would have to convince them to visit the website, typically by getting them to click a link in an instant messenger or email message that takes them to the attacker's website, and then convince them to click the specially crafted URL.</p> <p>The security update addresses the vulnerability by helping to ensure that SharePoint Server properly sanitizes user web requests.</p>
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Analysis
by VulDB Data Team • 02/25/2026
CVE-2020-16944 represents a critical cross-site scripting vulnerability within Microsoft SharePoint Server that arises from inadequate input sanitization mechanisms. This vulnerability falls under the Common Weakness Enumeration category CWE-79, which specifically addresses cross-site scripting flaws where untrusted data is improperly integrated into web pages without appropriate validation or encoding. The flaw exists in SharePoint Server's handling of user requests, where the system fails to adequately sanitize malicious input that could be embedded within web requests, creating an avenue for attackers to execute malicious scripts within the context of authenticated users.
The exploitation of this vulnerability requires an authenticated attacker who can craft specially designed requests to the affected SharePoint server. When successfully exploited, the vulnerability allows attackers to perform sophisticated cross-site scripting attacks that can execute arbitrary JavaScript code within the security context of legitimate users. This creates a severe operational impact as attackers can leverage the victim's authenticated session to perform unauthorized actions on the SharePoint site. The security implications extend beyond simple script execution to include data exfiltration, privilege escalation, and session hijacking capabilities that can compromise entire SharePoint environments.
The attack vectors for this vulnerability are diverse and can be executed through multiple delivery mechanisms. In email-based attacks, attackers craft malicious URLs that, when clicked by victims, trigger the exploitation. The most common scenario involves sending phishing emails containing specially crafted links that redirect users to compromised SharePoint sites. Web-based attacks require attackers to host malicious content on compromised websites or leverage existing websites that accept user-generated content. These attacks typically follow a multi-stage approach where users must first be convinced to visit an attacker-controlled website and then click on malicious links that ultimately exploit the vulnerability. The attack chain demonstrates the importance of user awareness and the need for robust input validation at all levels of web application processing.
The security update for CVE-2020-16944 addresses the core issue by implementing proper sanitization mechanisms within SharePoint Server's request handling processes. This remediation ensures that user-provided input is properly validated and sanitized before being processed or rendered within web pages, thereby preventing the injection of malicious scripts. Organizations should prioritize applying this security update immediately, as the vulnerability has been actively exploited in the wild and represents a significant risk to SharePoint environments. The fix aligns with Microsoft's security best practices and addresses the fundamental weakness in input validation that enables the cross-site scripting attack vector.
The operational impact of this vulnerability extends beyond immediate security breaches to include potential compliance violations and business disruption. Organizations using SharePoint Server must implement additional monitoring and detection measures to identify potential exploitation attempts, as the vulnerability can be used to steal sensitive information including browser cookies that may contain session tokens. The attack scenario also demonstrates the critical importance of implementing defense-in-depth strategies, including web application firewalls, content security policies, and user education programs to reduce the attack surface and mitigate the risk of successful exploitation. This vulnerability underscores the necessity of continuous security assessments and the implementation of secure coding practices to prevent similar issues in future software development cycles.